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Highlights Two-dimensional mono- and few-layered Ti 3 CNT x MXene nanosheets with extremely high nitrogen content were synthesized. Better performance for hydrogen evolution reaction (HER) than Pt/C catalyst in acidic, neutral and alkaline solutions. Exceptional performance of HER in both acidic and alkaline solutions. A large current density (> 500 mA cm −2 ) has been achieved for HER. Transition metal carbides, known as MXenes, particularly Ti 3 C 2 T x , have been extensively explored as promising materials for electrochemical reactions. However, transition metal carbonitride MXenes with high nitrogen content for electrochemical reactions are rarely reported. In this work, transition metal carbonitride MXenes incorporated with Pt-based electrocatalysts, ranging from single atoms to sub-nanometer dimensions, are explored for hydrogen evolution reaction (HER). The fabricated Pt clusters/MXene catalyst exhibits superior HER performance compared to the single-atom-incorporated MXene and commercial Pt/C catalyst in both acidic and alkaline electrolytes. The optimized sample shows low overpotentials of 28, 65, and 154 mV at a current densities of 10, 100, and 500 mA cm −2 , a small Tafel slope of 29 mV dec −1 , a high mass activity of 1203 mA mg Pt −1 and an excellent turnover frequency of 6.1 s −1 in the acidic electrolyte. Density functional theory calculations indicate that this high performance can be attributed to the enhanced active sites, increased surface functional groups, faster charge transfer dynamics, and stronger electronic interaction between Pt and MXene, resulting in optimized hydrogen absorption/desorption toward better HER. This work demonstrates that MXenes with a high content of nitrogen may be promising candidates for various catalytic reactions by incorporating single atoms or clusters.